It is typically the case that an optical signal transported on an optical fiber must be coupled from that fiber to or from another optical fiber or an electronic device. Typically, the end of the optical fiber is outfitted with an optical connector of a given form factor, which connector can be coupled to a mating optical connector on the other fiber or optoelectronic device. The optoelectronic device may be an optical-to-electrical converting device or an electrical-to-optical converting device. For instance, it is well known that optical signals are an extremely efficient method for transmitting data between two electronic devices. However, that optical data must be converted from electrical signals to optical signals at the transmitting device and then from optical signals back to electrical signals at the receiving device. Thus, optical signals usually start as digital electronic signals that are converted into optical pulses by an optical-to-electrical optoelectronic sub-assembly, typically, comprising at least a laser or LED that converts electrical signals to optical signals. Then, the optical signals are transmitted. The optical signals are received at a receiving device at the receiving end. The receiving device typically includes an optical-to-electrical optoelectronic sub-assembly having at least an optical detector, such as a photodiode, for converting optical input signals into electrical output signals.
It is well known in the optoelectronic arts to provide connectors with the optoelectronic sub-assemblies (either receiving or transmitting) incorporated directly in the connector.
These connectors generally must be fabricated extremely precisely in order to ensure that as much light as possible is transmitted through the connector. In a typical optical fiber, the light is generally contained only within the core of the fiber, which typically may be about 10 microns in diameter for a single-mode fiber or about 50 microns in diameter for a multi-mode fiber. A speck of dust typically is greater than 10 microns in cross section. Accordingly, a single speck of dust at the interface of two connectors can substantially or even fully block the optical signal from getting through the connector. Accordingly, it is well known to use expanded beam connectors in situations where it is likely that connections will be made in the field, and particularly in rugged or dusty environments, such as are frequently encountered in military and industrial applications.
Expanded beam connectors include optics that expand the beam so as to increase the beam's cross section at the optical interface of the connector (i.e., the end of the connector that is designed to be connected to another optical connector or optoelectronic device). Depending, of course, on the direction of light travel through the connector, an expanded beam connector may expand an input beam to a greater cross section and/or receive an input expanded beam and focus it to a smaller cross section. In theory, the expanded beam cross section is large enough so that dust particles will not substantially reduce the amount of light coupling between the mating connectors.
U.S. Pat. No. 6,913,402 discloses an expanded beam optical connector with a built-in optoelectronic sub-assembly as illustrated in FIG. 1. This connector 100 includes a ball lens 101 and a fiber 102 contained within a ferrule 103 positioned between the optical interface surface 111 and the optoelectronic sub-assembly 104. Using a receiving optical-to-electrical sub-assembly as an example, collimated light 113 entering the connector 100 at the optical interface surface 111 enters the ball lens 101 and is focused on the input end face 115 of the fiber 102. The other end face of the fiber 102 is in contact with an optical input 106 of an optoelectronic sub-assembly 104. The optoelectronic sub-assembly 104 outputs digital electrical signals on one or more electrical lines 107 corresponding to the optical signals striking the detector surface.
While the device of FIG. 1 is effective at focusing an expanded beam or vice versa, it is difficult and expensive to manufacture. Particularly, it comprises several optical pieces including a ball lens, an optical fiber, a ferrule, a housing, and an Optical Sub-Assembly, all of which must be assembled together precisely.